The present study addressed these methodological issues with a substantially larger sample than previous EEG asymmetry studies of depression, obtaining adequate power to examine whether relatively less left frontal activity would characterize individuals with any history of depression, and whether this effect might vary for men versus women. To reduce potential heterogeneity of depression, depressed participants included in the study met DSM-IV criteria for lifetime major depressive disorder (MDD) and endorsed no comorbid Axis I disorders with the exception of current dysthymia. Current depression was examined categorically (e.g., current MDD status) and dimensionally (e.g., by level of depressive questionnaire symptoms) to determine whether EEG asymmetry findings were simply due to elevated current symptomatology (indicating a state rather than a trait effect). To enhance the ability to identify trait-related variance associated with EEG asymmetry, resting EEG was recorded eight times, twice per day on four separate days within a two-week period to obtain a reliable measure of trait asymmetry for each participant. Moreover, asymmetry scores were calculated for four reference derivations (average, CSD, Cz, and linked mastoid) to examine whether depression-asymmetry
